BOlL. ACC. GIOENIA SCI. NAT. Catania 1993 The spermatozoon of Pseudoscorpions (Arachnida) CALLAINI G. & DALLAI R. Department ofEvolutionary Biology, Via P A. Mattioli 1-53100 Siena, Italy RIASSUNTO Questo studio riporta una indagine sulla struttura dello spermatozoo degli Pseudoscorpioni, basata essenzialmente su una tecnica di fissazione che consente una migliore conservazione dei microtubuli. In questo modo sono stati identificati tre modelli assonemali, il piu semplice dei quali e stato attribuito alle specie delle famiglie Chthoniidae e Neobisiidae. I dati ottenuti sono stati utilizzati per una discussione sui rapporti filogenetici all'interno degli Pseudoscorpioni e nella cIasse degli Aracnidi. Parole chiave: Spermatozoi, Psudoscorpioni, Filogenesi. ABSTRACT The present study describes new evidences on the ultrastructure of pseudoscorpion spermatozoa after tannic acid fixation. Three main axonemal models were observed: the simplest was found in Chthoniidae and Neobisiidae. Cheiridiidae, Atemnidae, Cheliferidae and Chernetidae have a 9+2 axoneme, surrounded by accessory sheaths, while Garypiidae and Olpiidae have a 9+9+2 axoneme. The phylogenetic significance of these results was discussed. Key words: Spermatozoa, Pseudoscorpions, Phylogeny. Introduction Reproduction in Pseudoscorpions is performed by indirect transfer of spermatozoa through spermatophores (WEYGOLDT, 1969). Spermato­ phores, show different degree of complexity, and contain a variable number of encysted spermatozoa. All the pseudoscorpion spermatozoa examined so far belong to the coiled-flagellate type (SOKOLOV, 1926; NESTER, 1932; TUZET et al., 1966; LEGG, 1973; BOISSIN, 1974; CAL­ LAlNI & DALLAI, 1984, 1987), a model which is also found in Araneids, Uropygi, Amblypygi and Ricinulei among Arachnida, and have essenti­ ally the same basic structure: an elaborated acrosomal complex that partially surround a condensed cylindrical nucleus, a pair of centrioles, elongated mitochondria, and a long flagellum. The main goal of this work is to give new insights on sperm ultra­ structure after preparation of pseudoscorpion spermatozoa with a new fixative (DAlLAI & AFZELIUS, 1990) that is known to give better pre­ servation of the microtubular structures. Materials and methods Pseudoscorpion species examined were: Chthonius ischnocheles, Chthonius tetracheLatus, Neobisium muscorum, Roncus Lubricus, Acan­ thocreagris itaLica, Garypus Levantinus, Geogarypus nigrimanus, Ga­ rypinus dimidiatus, AmbLyoLpium doLLfusi, CaLocheiridius oLivieri, Apo­ cheiridium ferum, RhacocheLifer macuLatus, HysterocheLifer tubercu­ latus, PseLaphochernes lacertosus, Allochernes wideri, Atemnus poLi­ tus. Males were dissected in phosphate buffer and testes were fixed according to DAlLAI & AFZELIUS (1990), to improve the visualization of microtubules. For freeze-fracturing the material was fixed for 30 min in 5% glutaraldehyde and 4% para formaldehyde in cacodylate buffer and infiltrated with a graded series of glycerol solutions. Fixed material was cooled with a graded series of glycerol solutions. Fixed material was cooled with liquid nitrogen and fractured at _115 0 C in a Balzer BAF 301 freeze-etching device. Samples were observed and photographed with a Philips CM10 electron microscope. Results Acrosomal complex The formation of the acrosome is a very complex process in pseudo­ scorpions, that in every species studied so far depends on the secretory activity of a large Golgi complex. The importance of Golgi activity du­ ring spermatogenesis first emphasized by SOKOLOW (1926) and NESTER (1923) at the light microscope, has been confirmed by transmission electron microscopical observations (BOISSIN & MANIER, 1967; WER­ NER & BAWA, 1988; DAlLAI & CALlAINI, 1990). 36 The process of acrosome formation starts with the positioning of a large Golgi complex, constituted by several densely packed cisternae, over the spermatocyte nucleus (Fig. 1). The secretory activity of these cisternae leads to the production of a large number of small vesicles that accumulate between the nucleus and the Golgi apparatus. Later, a large irregular vesicle filled with filamentous material takes contact with the anterior region of the early spermatid nucleus. The acrosomal material progressively increases its density in the axial part, and pushes off the acrosomal membrane in such a way that a kind of hook is formed. Later on the acrosomal membrane in close contact with the nuclear membrane forms an invagination in its central region and, at the same time, the nuclear envelope also begins to form an endonuclear cavity. This subacrosomal cavity, in which progressively amorphous dense material accumulates, corresponds to the perforatorium. During the formation of the primitive acrosomal vesicle the nucleus elongates and chromatin condenses in the apical region. Pore complexes, absent from nuclear envelope surrouding the condensed chromatin, are instead very numerous in the region overlapping the chromatin-free nucleoplasm (Fig. 2); it is suggesting that this region is still involved in metabolic traffic. The secretory activity of the Golgi apparatus also leads to the formation of a peculiar kind of ribbon that starts from the acrosomal vesicle and surrounds the nucleus in helicoidal fashion, moving toward its basal end. The proces of acrosome formation is essentially the same in all species of pseudoscorpions studied so far. However, the Geogarypus spermiogenesis develops with interesting variations, dealing with the great extension of the acrosomal helix. This structure forms at least three coils in the encysted cell (Fig. 3). In cross section the acrosomal material is stratified in layers to give origin to several laminae according to different planes; this feature is reminiscent of a crown (DAI1.AI & CALLAINI, 1983, 1990) (Fig. 4). Axoneme In early spermatocytes there is a single centrosome constituted by a pair of orthogonally arranged centrioles (Fig. 7). The centrioles move apart and organize the microtubules of the mitotic spindle that leads to the formation of two sister spermatids. In cross section, instead of the conventional triplets of most metazoan centrioles, only doublet micro- 37 tubules with A and B subtubules were found (Fig. 8). C-tubules, when visible are incomplete, and are formed by 3-4 protofilaments disposed in hook-like fashion. Tubules are embedded in the dense pericentriolar material. These aberrant centrioles persists in the young spermatid, when the pericentriolar material begins to organize dense projections, radially oriented (Fig. 9). At sperm maturity two coaxial, or obliquely arranged centrioles of different size are present (Fig. 10). The short proximal centriole is located in a nuclear invagination. The distal centriole, from which the axoneme originates, shows the usual feature of nine complete triplets of A- B-, and C-tubules with 13, 10, and 10 protofilaments re­ spectively (Fig. 11). Each triplet is embedde in a dense mass and is connected with an axial rod by a radial link. This structure gradually transforms in the basal part of the axoneme, and is characterized by 9 doublets devoid of arms and by two central tubules (Fig. 12). The basic structure of the axoneme, which is enclosed in a more or less evident flagellar tunnel, is essentially the same in the pseudoscorpion species examined so far. This consists of the well known 9+2 tubular pattern with well evident outer and inner dynein arms, radial links, nexin bridges, and dense central sheath that envelopes the inner pair of microtubules (Fig. 5). A- and B-tubules are formed by the conventional 13 and 10 pfs, respectively. The position of dynein arms on A subtubule is that described in many other flagellar axonemes, with outer arms projecting from the gap between pf. n° 13 and 14 and inner arm in that one between pf. n° 16 and 17 (Fig. 6). Little differences in axonemal morphology were recognized in the spermatozoa of the species that we have examined and three models can be described. The most simple model is that represented by tha axoneme of Chthonius, which is also found in Neobisium, Roncus, and Acantho­ creagris. In these cases the axoneme and the flagellar tunnel are only surrounded by cell membranes. Whithin this model Garypinus and Am­ blyolpium, show a greater complexity of the axonemal structure due to the presence of a fibrous cytoplasmatic dense material closely apposed to the plasma membrane (Fig. 13). The second model is found in several Cheliferidae species where a dense fibrous material forms a compact envelope that surrounds the flagellar tunnel. A thin sheath is also present around the axoneme (Fig. 17). The flagellar sheath is well developed in Chernetidae and Ante­ midae species, whereas it is lacking in Apocheridium (Fig. 16), and incomplete in Rhacochelifer and Hysterochelifer. In these latter species 38 the dense material adhering to the inner face of the flagellar mambrane, at the distal portion of the flagellum is fragmentated and reduces to nine small patches located externally to the peripheral axonemal doublets (Figs. 18, 19). The third axonemal model is found in Geogarypus, Garypus, and Calocheiridius (Fig. 14). In the proximal half of the axoneme of these species nine thin bundles of electrodense fibres adhere externally to the peripheral doublets, forming accessory structures (Fig. 15). Discussion Spermiogenesis in pseudoscorpions ends with a peculiar coiling process, that occurs before the spermatozoa are discharged in the lumen of the testis, where they appear surrounded by a secretory